MEASUREMENT OF DISSOLVED OXYGEN IN WATER USING GLASS-ENCAPSULATED MYOGLOBIN

摘要

Myoglobin (Mb)) encapsulated in a glass matrix by the sol-gel method was examined as; a sensing element for measurement of dissolved oxygen (DO) in water using electronic absorption spectroscopy in the visible region, The Mb-containing gel was porous and transparent, and the encapsulated Rib exhibited the same chemical and spectroscopic properties in the gel as in solution upon reduction of metMb with dithionite to give deoxyMb or absorption of DO to give oxyMb. The absorbance of a deoxyMb-containing gel changed linearly with time upon exposure to DO for the first 8 min, or longer, at three selected wavelengths, 418, 431.5, and 436 nm, The linear absorbance change rate was established in a few minutes, <5 min, and was directly proportional to the concentration of DO, which is found to be a unique property of the sol-gel glass-encapsulated Mb, The overall changes in absorbance at 431.5 and 436 mn were substantially larger than at 418 nm for a given DO concentration, and thus the correlation index was significantly higher at those wavelengths. The DO concentrations examined in this study ranged from 2 (25% air-saturated water) to 8 ppm (100% air-saturated water). These results indicate that the DO concentration can be determined quantitatively by observing the rate of change of the visible absorption spectrum of glass-encapsidated deoxyMb. This method does not require stirring of the water sample, Moreover, this method does not require the water sample to be exposed to a gaseous environment during the measurement, unlike the membrane polarographic oxygen detector method. Thus a glass-encapsulated Mb gel prepared by the sol-gel method isa practical sensing element for accurate and reproducible measurement of DO concentrations in water.